Freshwater Eel Species Research Articles

Stegodexamene anguillae (Digenea: Lepocreadiidae), an intestinal parasite of eels (Anguilla spp.) in New Caledonia

Adult trematodes of the genus Stegodexamene Macfarlane, 1951 were recorded from the intestines of two species of freshwater eels, the Pacific short-finned eel Anguilla obscura Günther and the speckled longfin eel Anguilla reinhardtii Steindachner from the Pouembout and La Foa Rivers, New Caledonia, South Pacific. They were identified as Stegodexamene anguillae Macfarlane, 1951, a species previously reported only from eels in New Zealand. The morphology of adult S. anguillae seems to be practically identical with that of the later described Stegodexamene callista Watson 1984 from eels in Australia. The finding of S. anguillae in A. obscura and A. reinhardtii in New Caledonia represents new geographical and host records. In addition to this trematode, two larval specimens of a cestode of the order Proteocephalidea were found in the intestine of one A. obscura from the Pouembout River. No monogenean was found in eels of New Caledonia.

Are morphological characters distinctive enough to discriminate between two species of freshwater eels,anguilla celebesensis andA. interioris?

To test the reliability of morphological keys for identifying two freshwater eel species,Anguilla celebesensis andA. interioris, mitochondrial DNA sequences were analyzed. Of eleven specimens examined, five were from Sulawesi and six from New Guinea. Specimens were morphologically identified as tenA. celebesensis and oneA. interioris. However, mitochondrial DNA sequence analysis indicated the existence of two genetically distinct groups, which corresponded exactly to the sampling localities. This contradiction might be attributable to inadequate descriptions of the anguillid species, for which intra-specific variations have been significantly underestimated. New approaches such as molecular analysis, are necessary for species’ identification of freshwater eels.

Seasonal arrival patterns of juvenile freshwater eels (Anguilla spp.) in New Zealand

The arrival season of glass eels of both New Zealand species of freshwater eel, the short‐finned eel (Anguilla australis (Richardson)) and the longfmned eel (A. dieffenbachii (Gray)), was studied by electric fishing of 13 streams/rivers throughout east and west coasts of both North and South Islands at 14‐day intervals. Sites were usually located at the most downstream riffle exposed at low tide, and sampled by single‐pass electro fishing. The species composition was dominated by shortfins, with exceptions being west coast sites, one in the North Island and two in the South Island. From a comparison of species proportions in adjacent catchments, it was concluded that glass eels make choices about entry in particular water‐types. As the stage of pigmentation advanced during the arrival season, “early stage” glass eels were defined and densities of these compared to show seasonal arrival patterns—densities were generally low in August, highest in September‐October, and declined during November‐December. Patterns of arrival varied from almost continuous in some streams to “intermittent” in others. Longfmned glass eels preceded shortfinned glass eels, and probably arrived in the North Island before the South Island; shortfinned glass eels showed the opposite trend. Possible migration routes to New Zealand are discussed.

Diet of two species of freshwater eel(Anguillaspp.) in Lake Pounui, New Zealand

Abstract Feeding habits of co‐existing populations of the freshwater eels, Anguilla australis Richardson (shortfinned eel), and A. dieffenbachii Gray (long‐finned eel) were studied in Lake Pounui, Wairarapa. A combination of sampling equipment gave a sample of 682 shortfinned eels and 310 longfinned eels ranging in length from 13 to 135 cm. Both species probably feed intermittently and are opportunistic feeders, consuming a wide range of food items, although feeding of individual eels was normally selective for a single prey species. Diet of each species changed with size. Smallest eels of both species ate mainly amphiphods and insect larvae; the snail Potamopyrgus antipodarum was the dominant food organism for shortfinned eels of 30–69 cm but was unimportant to longfinned eels. Longfinned eels > 40 cm were principally piscivorous but fish did not become an important part of shortfinned eel diet until eels were > 70 cm. At similar sizes, the two species had different diets. Eels of the same species but fr...

Environmental Correlates of the Freshwater Migration of Elvers of the American Eel in a Rhode Island Brook

The freshwater migration of elvers of the American eel Anguilla rostrata was continuously monitored at the freshwater interface and three locations in the lower stretches of a Rhode Island brook in 1980. Most elvers arrived at the freshwater interface in May and were incompletely pigmented. Although their initial arrival coincided with a large increase in water temperature, subsequent captures at the interface did not correlate with any measured environmental variable including water temperature, time of day, and tidal condition. Elvers appeared to delay upstream migration at the interface while experiencing behavioral and physiological changes. Two hundred meters above the interface, elvers were caught primarily at midday and capture records showed a significant 14.8-d periodicity corresponding to, but lagging behind, that of spring tides. The onset of upstream migration may have been triggered by changes in water chemistry caused by the intrusion of estuarine water during high spring tides. Further upstream, captures persisted through October and lacked both diurnal and 14.8-d periodicity. Migration in fresh water appeared highly stochastic; light and water temperature showed a weak positive correlation with some capture rates, and rain occasionally influenced migration at one location by altering river flow. The behavioral changes that elvers undergo during their entry into fresh water, coupled with the apparent influence of local hydrographic conditions on migration, may explain discrepancies among prior studies. The behavior of elvers of the American eel is similar to that of other species of freshwater eel.

Eels in Southern Africa

SPONSORED by the South African Council for Industrial and Scientific Research, this Department, under the direction of Prof. J. L. B. Smith, is undertaking the study of the life-history of the freshwater eels of the western Indian Ocean. Most authorities have hitherto held that only one species of freshwater eel, namely, Anguilla mossambica Peters, occurs in South Africa. Ege1 recorded a specimen of Anguilla marmorata Quoy and Gaimard, from the Buffalo River, Eastern Cape (27° 30′ E., 32° 57′ S.), but as this was the only one from the continent of Africa its validity has been queried. However, among the eels in this Department and of the Kaffrarian Museum, Kingwilliamstown, we have found six, all females, with pleated gonads full of ova, which are unquestionably Anguilla marmorata Quoy and Gaimard. Three of these, 85–135 cm. in length, are from the Keiskama River (27° 13′ E., 33° 03′ S.) (near the Buffalo), and the remainder, 73–108 cm. in length, from the confluence of the Sabi and Lundi Rivers in Southern Rhodesia (32° 25′ E., 21° 10′ S.). In both cases the habitats are mature rivers below the 1,000-ft. contour.